The present invention relates to the use of adaptive arrays in communications receivers and is particularly directed to reducing the number of tuner components, space requirements, energy consumption and improved performance of the adaptive array.
A common problem in communications is the corruption of the received signal by multipath, co-channel, adjacent channel or other interference that reduces reception quality. One approach well known in the art for reducing the effects of multipath and other interference is the adaptive array (see for example, Widrow, B. and others, xe2x80x9cAdaptive array Systemsxe2x80x9d, Proceedings of the IEEE, Vol. 55, No. 12, December 1967, pp. 2143-2159; Monzingo, Robert A. and Miller, Thomas W., Introduction to Adaptive Arrays, John Wiley and Sons, New York, 1980; U.S. Pat. Nos. 4,736,460 and 4,797,950 by Kenneth Rilling).
One problem with current adaptive arrays is that they require a large number of tuner components that occupy space, consume power, generate heat and cause inconsistencies from antenna channel to antenna channel. This can be a particularly significant problem for physically small and battery powered portable receivers. In many communications systems, the received desired signal has signals in adjacent frequency channels or adjacent frequency bands. To reduce the interference from these adjacent channel and adjacent band signals, bandpass filters or tuning bandpass filters are used to select the frequency channel of the desired signal and reject the adjacent channel and adjacent band signals. Typically for an adaptive array with N antennas, N tuners are used, where a tuner typically includes a bandpass filter (tuning bandpass filter) and a pre-amplifier. If the adaptive array is implemented at IF (intermediate frequency), each tuner includes a mixer to down convert the RF (radio frequency) signals to IF. Reducing the number of tuners required by the adaptive array increases the value of the adaptive array in solving a receiver interference problem, particularly in physically small and battery powered portable receivers. Reducing the number of tuners also reduces the inconsistencies from antenna channel to antenna channel. An additional problem with many current adaptive array implementations is that they can be difficult to use with direct down conversion receivers without compromising the advantage of lower cost.
The present invention reduces the number of tuners required by an adaptive array in an environment with signals outside the selected channel bandpass from N to one. Signals received by the N antennas are split and delayed in time by a tapped delay line, weighted and summed at RF. The summed signal is then bandpass filtered to remove signals outside the selected channel bandpass to generate the adaptive array output signal. The adaptive array output signal is coupled to the feedback function to generate the feedback signal. The first input signal to each weight calculator is the associated time delayed wideband signal derived from the associated antenna. The feedback signal is then coupled as the second input signal of each weight calculator for generating the weight value. The signals outside the frequency bandpass of the selected channel are uncorrelated with the components of the feedback signal. As a result, the signals outside the selected channel bandpass do not contribute to the value of the weight, causing the adaptive array to use its degrees of freedom to reject interference in the selected channel bandpass, similar to an adaptive array with N tuners.
In another embodiment of the present invention the summed signal is down converted to IF by a down converter mixer to generate the IF summed signal. The IF summed signal is to the IF bandpass filter, to remove all IF signals outside the bandpass of the selected channel. The output signal of the IF bandpass filter is applied to the IF feedback function to generate the IF feedback signal. The IF frequency is the same for all selected channels. The IF feedback signal is then up converted by another mixer back to the RF frequency of the selected channel RF feedback signals. The output signal of the up converter is coupled as the second input signal of each weight calculator. Each weight calculator correlates the feedback signal with the associated wideband signal from the output of the associated tapped delay line to generate the weight value.
The present invention reduces the number of tuners, space requirements, and power requirements.